This invention relates to a turbine engine segment, such as a turbine blade outer seal.
A turbine blade outer air seal (BOAS) seals radial leakage around blade tips in the gas path of a turbine engine. Typically, the seal is made in circumferential panels or segments that are hooked to the engine case. These segments form a circular seal around the gas path. Due to the high temperature of the gases coming from the combustor of the turbine engine, BOAS segments are provided with cooling passages through which cooling air flow is passed often in a circumferential direction.
To form the cooling passages in the BOAS segment castings, ceramic cores are used. The BOAS segment is cast around the ceramic core and the core is then leached out leaving behind a cooling passage within the BOAS segment. These cores are also provided with turbulators, known as trip strips, that create ripples within the cooling passages so as to promote turbulent airflow through the passage, which improves the heat transfer rate and its cooling performance.
The ceramic cores themselves are formed in a separate die by injecting a ceramic slurry therein. The cores remain in the die for some time, until they have developed enough strength to be removed. To eject the cores from the dies without breakage, the cores are designed with a land to receive an ejection pin. When the ceramic cores are then used to create the cooling passages within the BOAS segment casting, these lands are then reproduced as part of the cooling passage. However, these lands preclude the formation of trip strips at their location. In the past, these lands have been located in the middle portion of the BOAS segment. Due to the absence of trip strips at the location of the land in the middle of the BOAS segment, the BOAS segment becomes susceptible to thermal mechanical fatigue (TMF). TMF may lead to cracking, which reduces the life of the part and is not desirable.
A need therefore exists for an improved design for the BOAS segment that eliminates or reduces the prospect of cracks caused by thermal mechanical failure.